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1 November 20, 2013 Heather Sustersic Dear Professor Sustersic, The following technical report was written to fulfill the requirements specified in the Structural Technical Report 4 assignment that was handed out on October 23, Technical report 4 includes a complete lateral analysis of the New Library at the University of Virginia s College at Wise, located in Wise, Virginia. This analysis includes information gathered using 3D modeling software, critical member spot checks for strength, maximum drift and story drift checks under wind and seismic loading, and overturning moment/foundation impact. Thank you for reviewing this report. I look forward to discussing it with you in the future. Sincerely, Macenzie Ceglar Enclosed: Technical Report 4

3 Technical Report 4 Macenzie Ceglar Structural Option Executive Summary The New Library at the University of Virginia s College at Wise will serve as a main link between the upper and lower campus areas, which are currently divided by a steep 60 foot hill. The new 6 story, 6,000 ft 2, library will be integrated into the hillside, and will provide students with an easier and safer path across campus. The architectural design of the façade incorporates traditional materials found on campus, such as brick and stone. Construction on the New Library began in August 2012 and will be completed in August Soil loads caused the foundation system for the New Library to be unique in its design. The foundation system utilizes a temporary leave-in-place soil retention system and foundation walls which are designed to resist future lateral soil loads. Other parts of the foundation system include piers, footings, and slabs-on-grade. All six stories of the building have composite floor framing involving both composite steel wide flange members and composite decking. Framing layout in the building is fairly typical with bay sizes ranging between 25-4 x 25 4 and 31-0 x Steel wide flange columns are used as the vertical framing system and shear walls make up the building s lateral system. Loading conditions considered in the building s design include live loads, gravity loads, snow loads, wind loads, seismic loads, and lateral soil loads. The Virginia Uniform Statewide Building Code (USBC); along with Facility Design Guidelines, governs the design of all buildings on the campus. The USBC adopts chapters 2-35 of International Building Code (IBC) 2009, which references codes and standards which include American Society of Civil Engineers (ASCE) 7-05, American Concrete Institute (ACI) 31-0, and the 13 th edition of the Steel Construction Manual. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 1

42 Technical Report 4 Macenzie Ceglar Structural Option Lateral Computer Model For this technical report a 3D computer model was created using ETABS, and was used to distribute the story forces to each lateral element. This model was also used to determine the maximum drift and story drifts due to each load case. Figure 1: 3D View of ETABS Model Overview The lateral system used in the New Library is ordinary reinforced shear walls. The seven individual shear walls are shown in red in Figure 1 above, while the diaphragms for each level are shown in gray. These seven shear walls can be located on the floor plan provided in appendix A where they are numbered 1-7. All of the shear walls are 12, with the exception of shear wall 1 and 2 which are 16 and 33 at the base level. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 40

43 Technical Report 4 Macenzie Ceglar Structural Option Modeling Decisions Due to the large soil loads on the structure, the design involves a significant number of foundation walls. For this analysis, only the shear walls were modeled. This modification was made in order to be able to analyze the shear walls under the full lateral forces without the foundation walls providing increase lateral resistance. The foundation walls are designed to act as either a pined or fixed connection at the base with supports at each floor level. Due to this design, the soil forces were still used in the analysis of the building s lateral system, even though no foundation walls were modeled. The shear walls were modeled as membranes. Membranes have no out-of-plane stiffness and therefore will take no out-of-plane shear forces. Shear wall 1, 2, 5, 6, and 7 were modeled with pin supports at the base. In the structure these shear walls are supported either by strip footings with spread footings at each end, or just by strip footings. These base conditions do not justify the use of a fixed connection in the model. Shear walls 3 and 4 were modeled with fixed supports at the base. In the structure these shear walls rest on a mat foundation that is located in the North-East corner of building. This base condition justifies the use of a fixed condition in the model. The diaphragm was modeled as rigid. This allowed the transfer of lateral forces to the shear walls without providing extra resistance. The floor system in the New Library is a composite floor system which has limited flexibility and allows the lateral forces to be transferred to the shear walls. The openings in the diaphragm and shear walls were not modeled. This was due to the complexity of modeling openings accurately, especially those which are located in close proximity to lateral elements. This decision had minimal negative impact on the model due to the fact that no masses were used in the model. All of the wall sections were modeled to consider the effects of cracked sections on the deflection of the lateral system. Per ACI , the member stiffness maybe modified through section properties which decreased the wall section stiffness by 65%. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 41

44 Technical Report 4 Macenzie Ceglar Structural Option Verification of Model Before using the lateral model to distribute the shear forces to the shear walls, the model was checked to determine if it was reporting accurate data. This was done by applying a 1000 kip load in the x-direction to the center of mass at the roof level. The first verification was of the story forces and story moments, shown in Figure 2. This was done to make sure that each story was receiving 1000 kips and each story was receiving a moment equal to 1000 multiplied by the story s distance from the roof level. Figure 2: Story Forces and Moments The next verification was that of the in-plane shear force contours, shown in Figures 3 and 4. It was verified that the three shear walls acting in the x-direction had the largest contour lines due to the direct shear forces, while the remaining four shear walls had minimal contour lines due to torsional shear forces. Figure 3: Shear Force Contours In-Plane Shear Wall Figure 4: Shear Force Contours Lateral System U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 42

45 Technical Report 4 Macenzie Ceglar Structural Option The last verification was a brief check of the distribution of forces to each lateral element at level 2. Distribution In order to check the distribution of forces, the relative stiffness of each element was calculated. The tables below show the relative stiffness of each shear wall along with the forces from ETABS. Figure 5 below shows the direction of direct shear forces and torsional shear forces in shear walls 2, 4, and 6. Based on the relative stiffness of each shear wall, it is expected that SW2 would have the highest shear forces followed by SW 6 and 4 respectively. The shear forces from the model match this expectation. It is also important to notice that the torsional shears will cause the shear in SW2 to decrease while increasing the shear in SW4 and SW6. The shear forces from the model also match these expectations. Shear Wall Relative Stiffness of Shear Walls E (ksi) h (in) b (in) t (in) k (K/in) Relative K X Direction Shear Forces from ETABS Shear Wall Shear Force (k) SW4 SW6 1000K CM CR SW2 Figure 5: Direction of Shear Forces U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 43

46 Technical Report 4 Macenzie Ceglar Structural Option Summation of Forces The equilibrium of the model was then verified in both the x and y directions. Figure 6 below shows the shear forces in each shear wall in the model K K K K 1000K CM CR K K 51.2 K Figure 6: Direction of Shear Forces F x = = 0 F y = = 0 Torsional Forces (With Respect to CR) It was also important to notice that the torsional shears were in the correct direction with respect to the center of rigidity. The offset between the center of mass and center of rigidity will cause a clockwise rotation. All shears to the left of the CR are in the Y direction and all shears to the right of the CR are in the +Y direction. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 44

47 Technical Report 4 Macenzie Ceglar Structural Option Building Properties Below is a table showing the location of the center of mass for each level of the New Library. The center of mass for each level was calculated by hand, and the excel spread sheets are included in appendix B. ETABS is able to calculate the center of mass for the structure, but this requires the mass of the structure to be included in the program. Due to the fact that this was strictly a lateral model, and no gravity elements were included, no masses were to be added to the model. The center of mass was used in the application of seismic forces. Center of Mass Level X-Direction Y-Direction Roof Below is a table showing the location of the center of rigidity for each level of the New Library. ETABS calculates the center of rigidity of each level in the model. A spot check of the center of rigidity is included in appendix B of this report. Center of Rigidity Level X-Direction Y-Direction Roof Below is a table showing the location of the center of rigidity for each level of the New Library. ETABS calculates this location automatically when a wind load is applied, and the locations were verified. Center of Pressure Level X-Direction Y-Direction Roof U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 45

53 Technical Report 4 Macenzie Ceglar Structural Option Seismic Forces The seismic forces determined in technical report 2 were expanded upon to include accidental torsion. ASCE requires that when the diaphragm is not flexible, the design for seismic forces shall include the accidental torsional moment caused by the assumed displacement of the center of mass each way from its actual location by a distance equal to 5 percent of the dimension of the structure perpendicular to the direction of the applied forces. Due to the fact that the building is assigned to seismic category B, ACSE states that seismic forces are permitted to be applied independently in each of two orthogonal directions and orthogonal interaction effects are permitted to be neglected. The amplification factor Ax is also taken as 1.0 due to the building being assigned to seismic category B. Below are tables showing both the applied forces and moments. Level Height Total Weight (K) Calculation of Story Forces - EW-Direction w i h i k (K-FT) C vx f i (K) V i (K) B y (Ft) 5% B y A x (K) M z (Ft-K) Roof SUM: Level Height Total Weight (K) Calculation of Story Forces - NS-Direction w i h i k (K-FT) C vx f i (K) V i (K) B x (Ft) 5% B x A x (K) M z (Ft-K) Roof SUM: U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 51

54 Technical Report 4 Macenzie Ceglar Structural Option Building Irregularities The New Library was inspected for vertical and horizontal irregularities. It was determined that no vertical structural irregularities applied, but horizontal irregularity Type 1b and Type 4 did apply (shown in Figure 11 below). Figure 11: Horizontal Structural Irregularities The impact of these irregularities was considered to an extent for this report, but will have to be considered and further expanded upon in the spring semester proposal. One thing to further explore would be the foundation walls impact on the story drifts. These walls add a significant amount of stiffness to the structure and may eliminate the extreme torsional irregularity. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 52

55 Technical Report 4 Macenzie Ceglar Structural Option Lateral Earth Pressures The Library at the University of Wise Virginia s College at Wise has a unique condition in which it is integrated into the existing 60 foot hillside. For this technical report the impact of the soil loads on the structures lateral system were considered using an equivalent fluid pressure of 47 PCF provided in the geotechnical report. Below are tables showing the applied soil loads, and detailed tables are provided in appendix C. It is also important to note that in this report the soil loads were strictly used as an applied lateral load. They do not serve a role in aiding the building it terms of drift control, and were not considered to be causing drift. East Elevation: Lateral Soil Forces(K) Level Column Line AC Column Line CC1 Column Line C1D1 Column Line DE North Elevation: Lateral Soil Forces(K) Level Column Line 13 Column Line 35 Column Line 57 Column Line 7 Column Line South Elevation: Lateral Soil Forces(K) Level Column Line 13 Column Line 36 Column Line 67 Column Line 7 Column Line University of Virginia s College at Wise New Library Page 53

56 Technical Report 4 Macenzie Ceglar Structural Option Member Spot Checks for Strength As part of the lateral analysis of the New Library the lateral system was spot checked for strength. Shear walls that were critical members, those taking the highest amount of shear force, where to be checked. The largest shear forces occurred at the base level of the shear walls, so each shear wall was checked for each load case at this level. These comparisons can be seen in the excel tables in appendix D. It was determined that shear wall 2 was the wall with the highest shear forces. The concern with this wall was that even though it takes the most shear force it is also significantly thicker than the common shear walls. Thus, shear wall 6 was also checked due to the fact that it had the second highest shear forces and a typical thickness of 12. Max Shear: 265 K Max Shear: 1634 K Figure 12: Moment Diagram for Shear Wall 2 Figure 13: Moment Diagram for Shear Wall 6 The largest shear forces in both the x-direction and y-direction were caused by soil loads. Thus, soil loads dictated the controlling load combination for the analysis of the shear walls. It was determined that load combination 7 from IBC 2009 was the controlling combination: 0.9D + 1.0E + 1.6H The following pages show the hand calculations for determining the controlling load combination along with the member spot checks. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 54

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65 Technical Report 4 Macenzie Ceglar Structural Option Drift Checks Drift Due to Wind A check of the maximum drift of the structure under service wind loads was checked based on the industry accepted value of H/400. The overall height of the structure is 102 feet resulting in an allowable drift of 3.06 in. The following table shows the maximum drift due to each load case produced by the ETABS model and its comparison to the standard. The maximum drift of the structure was at the roof level. Load Case Wind Load Cases Maximum Drift (in) Allowable Drift (in) Pass/Fail Wind Case 1 X-Direction PASS Wind Case 1 Y-Direction PASS Wind Case 2 X-Direction (+M) PASS Wind Case 2 X-Direction (-M) PASS Wind Case 2 Y-Direction (+M) PASS Wind Case 2 Y-Direction (-M) PASS Wind Case PASS Wind Case 4 (+Moments in Same Direction) PASS Wind Case 4 (-Moments in Same Direction) PASS Wind Case 4 (+Moments in Opposite Direction) PASS Wind Case 4 (-Moments in Opposite Direction) PASS Discussion of Results: The lateral system passes for all of the applied wind loading cases, and is adequate to resist the wind loads based on the serviceability criteria of H/400. This was expected due to the fact that wind loads were not the controlling load case. One thing to notice about the result is that the largest drift is due to shear wall 4 (seen on plan in appendix). This particular shear wall is connected to one of the foundation walls that were not modeled. If the other wall was modeled it would have provided increased stiffness to this wall and the drift in this wall would have been decreased. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 63

69 Technical Report 4 Macenzie Ceglar Structural Option Impact on Foundations: The foundation of the New Library consists of individual spread footings and continuous strip footings, both of which will bear on bedrock. The foundation would be to be checked for base shear and overturning moment due to the maximum load condition. The controlling load combination for the foundation design would most likely be load combination 7 from IBC 2009: 0.9D + 1.0E + 1.6H This is due to the fact that the soil loads cause the largest base shear and overturning moment, while seismic loads cause the second largest base shear and overturning moment. The foundation walls in the New Library had little impact on this technical report, but the soil loads had the largest impact of all the load cases. It is also important to note that the soil loads impacted the strength and overturning moment checks, but were not considered in the drift checks. This is important because often the drift/deflection is what often controls a design. These results are a prime example of why the unique condition of the hillside cannot be overlooked in the foundation design. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 67

70 Technical Report 4 Macenzie Ceglar Structural Option Conclusion Technical report 4 consisted of a lateral systems analysis of the New Library at the University of Virginia s College at Wise Virginia. The content consisted of an overview of the lateral model used for the distribution of forces, lateral wind, seismic, and soil forces, member spot checks, drift checks, and overturning/foundation considerations. ETABS was used to create a lateral model which was used to distribute the forces to each lateral element. The building s design includes a large number of foundation walls, but in order to analyze the shear walls under the full lateral load the foundation walls were not included in the model. The model was verified including spot checks of shear contours and shear force distribution. The lateral system was checked under wind, seismic, and soil loads. Soil loads resulted in the largest shear forces in the shear walls in both the x and y directions. Member spot checks were completed for two critical shear walls for the criteria of strength. Load combination seven from ASCE7-05 was determined to be the controlling load combination for both shear walls. Both shear walls passed the spot checks. Drift checks were completed for both wind and seismic service loading conditions. The lateral system passed for both checks. Overturning moments and the impact on the foundation of the building was considered. Soil loads resulted in the largest over turning moment in both the x and y directions. It was verified that the resisting moment of the building was sufficient in both directions. Due to the large soil loads, it was determined that they will have a significant impact on the foundation. This confirmed the use of a significant amount of foundation walls used in the foundation design of the new library. After completing a lateral system analysis of the New Library it was determined that the lateral system is sufficient to resist all lateral loading conditions. U n i v e r s i t y o f V i r g i n i a s C o l l e g e a t W i s e N e w L i b r a r y Page 6

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